This invention relates generally to air samplers and, more particularly, to an air sampler assembly for collecting airborne pathogens and psychrometric data from a room or remote locations wherein the sample volume is electronically controlled.
The air inside buildings often is contaminated with particles and chemicals that adversely affect the health of the occupants. These pollutants have been brought indoors from the outside or arise from sources indoors. Airborne pathogens, sometimes referred to as biological contaminants or aerosols include;
1. Infectious agents such as bacteria, viruses, and fungi which may cause tuberculosis; legionellosis; Pontiac fever; measles; influenza; colds; aspergillosis; coccidioidomycosis; histoplasmosis; and
2. Allergenic agents such as bacteria, fungi, insects, algae, pollen, animals, and products of microbiological metabolism that may cause sensitivity to B. subtills; allergic asthma; rhinitis; hypersensitivity to molds; sensitivity to house dust mites, cockroaches, houseflies, moths, carpet beetles, aphids, crickets, mosquitoes, and weevils; hypersensitivity reaction to endotoxins from gram-negative bacteria, cotton dust (some mycotoxins are potent carcinogens); hayfever from ragweed pollen; sensitivities to grass and tree pollens; and allergic rhinitis and asthma from bird and mammal dusts.
The pathogens often manifest themselves as human health symptoms such as mucus membrane irritation, headache, and fatigue. These symptoms are associated with what is termed the xe2x80x9csick building syndrome.xe2x80x9d Biological aerosols have been the predominant cause of complaints in 1-5% of problem office buildings investigated by the U.S. National Institute for Occupational Safety and Health (NIOSH). Airborne biological contamination may be a larger problem in homes where there is a greater variety of source materials and very different types of activities that contribute to the presence of microorganisms, and plant and animal matter.
Assessment of biological aerosols in studies of indoor air quality requires knowledge of many specialties because complaints may be due to aerosols of bacteria, viruses, fungi, algae, house dust mite particles, or pollen grains. One may also need advice from epidemiologists, statisticians, and from medical professionals to diagnose infections and allergies. An understanding of ventilation systems and the movement of air through buildings is also essential, as is a knowledge of how small particles travel through the air and how they can be collected, identified, and quantified. Psychrometric properties of air such as relative humidity, absolute humidity, and dry bulb temperature help determine ambient conditions suitable for growth of pathogens. Building pressurization information helps identify the pathogen source and subsequent remediation options.
A vast array of sampling instruments has been developed for airborne microorganisms. A summary of a number of devices of this type can be found in Air-Sampling Instruments for Evaluation of Atmospheric Contaminants, 8th Edition (1995), American Conference on Governmental Industrial Hygienics. Two of these instruments, the Andersen cascade impactor and the all-glass impinger, have proven useful and reliable enough to be considered standard sampling instruments. The Andersen cascade impactor has remained popular, because it is convenient to use pre-poured plates, the distribution of particle sizes can be determined, and the sampling rate is fairly high (28 L/min). Liquid impingers are used when the organisms require rapid rehydration, to collect soluble materials, e.g., Tyco- or bacterial endo-toxins and some antigens, or when the total number of cells must be determined rather than the number of contaminate particles. Readily-identifiable pollen grains, algal cells, fungal spores, and fragments of nonviable organisms can be collected with a rotorod sampler or on air filters for identification with a light or electron microscope.
After suspended particles have been collected on or in a suitable medium, the viable microorganisms, those that will multiply when provided the appropriate conditions, contained in or on these particles can then be counted and identified. The techniques used to extract viable cells and particles carrying them from the air are also used by environmental scientists looking for nonviable particles. The most efficient methods of removing suspended particles from the air, e.g., filtration through fine pore matrices, might be adequate for resistant forms of microorganisms, such as spores, but can damage less environmentally resistant, vegetative cells. The absence of these sensitive cells from a sample could cause one to mistakenly conclude that they were not present in the environment sampled. The total number of cells present can be estimated by microscopic examination of collected dust, sometimes with the help of stains or fluorescent tags. NIOSH has suggested the following indoor concentrations of bacteria and fungi as indicative of situations deserving of further attention: air concentration greater than 103 colony-forming units per cubic meter (cfu/m3), dust samples greater than 105 cfu/g, water samples  greater than 105 cfu/ml.
The proposed NIOSH sampling protocol uses the last stage of the Andersen impactor to collect samples onto standard petri dishes of medium. Different media are used for collecting fungi and bacteria. The total number of viable particles is reported, and when useful, the isolates are identified. This procedure will identify cases of heavy contamination, but further tests might be needed in some situations. A more comprehensive approach would include using a spore trap with visual identification of spores and pollen in the collected dust, a viable sampler with at least three types of culturing media, and a filter or a liquid impinger sample for bioassays, biochemical tests, and immunological analyses.
The accurate measurement of the gas flow rate is very important in air filter sampling because the contaminant concentration is determined by the ratio of the sampled contaminant quantity to the sampled air volume. One widely used conventional flowmeter in air sampling is the rotameter. Rotameters are sensitive to pressure changes in upstream and downstream airflows. Most flowmeters are calibrated at atmospheric pressure, and many require pressure corrections when used at other pressures. When the flowmeter is used in air sampling, it should be downstream of the filter to exclude the possibility of sample losses in the flowmeter. Therefore, the sampled air is at a pressure below atmospheric due to the pressure drop across the filter. Furthermore, if the filter resistance increases due to the accumulation of dust, the pressure correction is not a constant factor. During the sampling period, the filter tends to be plugged and the flow rate may decrease as filter resistance increases. These factors make it difficult to measure the flow rate accurately.
Critical orifices have been widely used in flow rate control for air sampling because they are simpler, reliable and inexpensive. When the pressure drop across the critical orifice is more than 47% of the upstream pressure, the speed of sound is achieved in the throat and the velocity will not change with a further reduction in downstream pressure. Under these conditions, the flow rate is kept constant if upstream conditions are constant. However, commercially available orifices were found to lack the required precision and accuracy because they differed from the nominal flowrate by up to 15%. Another disadvantage of most critical orifice designs is that a pressure drop in excess of 47 kPa is required to ensure a stable flow. To achieve this pressure drop, a special high power vacuum pump must be used. Some commercial flow limiting orifices even require a vacuum as high as 72 kPa.
A portable device and method for collecting an electronically controlled sample of air that impacts a pathogen dish mounted substantially transverse to the overall airflow pattern to capture airborne pathogens and further having a psychrometric sensor that measures psychrometric properties of the air sample. Particulates in the air are caused to impact the surface of the growth/inhibitor media contained in the pathogen dish thereby depositing pathogenic microorganisms in the media. The growth/inhibitor media may be a solid, liquid, gel, or mixture thereof. A chip-based sensor measures psychrometric properties of the air sample.
Room air is sampled through a calibrated perforated impactor plate. Remote air samples are collected through a calibrated remote sensor assembly.
An advantage of the invention is the means for controlling the sample volume wherein the fan is activated and controlled for a predetermined time period programmed for the specific type of sample being collected. Each remote collection assembly and each room air collection assembly has a specific control algorithm designed for the entire collection device. All components are low airside pressure drop items to enable using of a small, low power fan.
Another advantage of the invention is the ability to collect airborne pathogen data and psychrometric data simultaneously thereby providing more complete information on the quality of the air being sampled.
Another advantage of the invention is that the sampler is simple, inexpensive, and portable. Rechargeable battery power allows the sampler to be used at any location and multiple samples can be drawn with a single battery charge. Each sample may contain a different growth/inhibitor media for collection of spores, pollen, dust, pathogens, and bioassays.